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Dryad

Widespread convergence towards functional optimisation in the lower jaws of crocodile-line archosaurs

Rawson, James1; Deakin, William1; Stubbs, Thomas2; Smith, Thomas3; Rayfield, Emily1; Donoghue, Philip1

Published Jul 17, 2024 on Dryad. https://doi.org/10.5061/dryad.dbrv15f6n

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Jul 17, 2024 version files 859.07 MB

Abstract

Extant crocodilian jaws are subject to functional demands induced by feeding and hydrodynamics. However, the morphological and ecological diversity of extinct crocodile-line archosaurs is far greater than living crocodilians, featuring repeated convergence towards disparate ecologies including armoured herbivores, terrestrial macropredators, and fully marine forms. Crocodile-line archosaurs therefore present a fascinating case study for morphological and functional divergence and convergence within a clade across a wide range of ecological scenarios. Here we build performance landscapes of two-dimensional theoretical jaw shapes to investigate the influence of strength, speed and hydrodynamics in the morphological evolution of crocodile-line archosaur jaws, and test whether ecologically convergent lineages evolved similarly optimal jaw function. Most of the 243 sampled jaw morphologies occupy optimised regions of theoretical morphospace for either rotational efficiency, resistance to Von Mises stress, hydrodynamic efficiency or a trade-off between multiple functions, though some seemingly viable shapes remain unrealised. Jaw speed is optimised only in a narrow region of morphospace whereas many shapes possess optimal jaw strength, which may act as a minimum boundary rather than a strong driver for most taxa. Functional convergence is common, with repeated evolution of shapes linked to specialised ecological roles including gracile jawed piscivores and more robust jawed herbivores.